Brief History of Computers
Generations of Computers
- Vacuum tubes - 1946-1957
- Transistors - 1958-1964
- Small-scale integration - 1965 on
- Up to 100 devices on a chip
- Medium scale integration - to 1971
- 100-3,000 devices on a chip
- Large-scale integration - 1971-1977
- 3,000 - 100,000 devices on a chip
- Very large scale integration - 1978 -1991
- 100,000 - 100,000,000 devices on a chip
- Ultra large scale integration – 1991 -
- Over 100,000,000 devices on a chip
The Second Generation: Transistors
- Replaced vacuum tubes (they generate heat, were bulky, unreliable)
- Smaller
- Cheaper
- Less heat dissipation
- Solid State device
- Made from Silicon (Sand)
- Invented 1947 at Bell Labs
- William Shockley et al.
Improvements in the Second Generation
‘Computer generations’ are classified based on the fundamental hardware technology employed e.g. transistors.
Each new generation is characterized by greater processing performance, larger memory capacity, and smaller size than the previous one.
Also, the second generation saw the introduction of more complex arithmetic and logic units and control signals, the use of high-level programming languages, and the provision of system software with the computer.
‘System software’ provides the ability to load programs, move data to peripherals, and to perform common computations, similar to Windows.
Transistor Based Computers
- Second generation machines
- NCR & RCA initially produced small transistor machines
- IBM 7000 series came later
- DEC (Digital Equipment Corporation) - 1957
- Produced its first computer PDP-1
- This computer and this company began the mini-computer phenomenon that became so prominent in the third generation.
The Third Generation: Integrated Circuits (ICs)
A single transistor is a discrete component.
Throughout 1950 these discrete components were manufactured separately, packaged in their own containers, and soldered together onto circuit boards, which were then installed in computers. The addition of a new transistor has to be soldered again on circuit board.
The entire manufacturing process, from transistor to circuit board, was expensive and cumbersome.
In 1958 came the achievement that revolutionized electronics and started the era of electronics: the invention of the integrated circuit.
It is the integrated circuit that defines the third generation of computers.
Micro-Electronics
Literally means “small electronics” has tremendously improved speed.
There has been a consistent trend toward the reduction in the size of digital electronic circuits thus leading to ‘microelectronics’.
A computer is made up of (logic) gates, memory (storage) cells and interconnections.
The integrated circuit uses the fact that such components and paths can be fabricated onto a semiconductor such as Silicon wafer (Chip).
To fabricate an entire circuit in a tiny piece of silicon, in this way many transistors can be produced at one time on a single wafer of silicon.
A relationship among Wafer, Chip, and Gate
- A thin wafer of silicon is divided into a matrix of small areas, a few millimeters square.
- The identical circuit pattern is fabricated in each area, and the wafer is broken up into chips.
- Each chip consists of many gates and/or memory cells.
- These chips can be connected on a PCB to produce complex circuits.
Moore’s Law
Gordon Moore, co-founder of Intel, in 1965 presented his famous law.
Moore observed that the number of transistors that could be put on a single chip was doubling every year (12 months).
Furthermore, he predicted that this pace would continue into the near future. The predicted increased density of components on a single chip.
To the surprise of many, the pace continued year after year and decade after decade.
The pace slowed to a doubling every 18 months in the 1970s but has sustained that rate ever since.
Consequences of Moore’s Law
- The consequences of Moore’s law are profound:
- Cost of a chip has remained almost unchanged during this period of rapid growth in chip density.
- Higher packing density means shorter electrical paths, giving higher performance, increased operating speed.
- Smaller size gives increased flexibility. (more suitable to fit in the home)
- Reduced power and cooling requirements.
- Fewer interconnections increase reliability.
Growth in CPU Transistor Count
Improvements that Came with IC Designs
Since the geometric sizes of components (transistors) are small, the time delays for signal propagation are short.Components being small consume less power and dissipate less heat, the circuit is thermally stable.
Every semiconductive component within an IC has virtually identical operating parameters, device mismatches are less.
This means that at high clock rates! All skew times, delay times, hold times... Everything is fixed and predictable!
The components being small can switch states at a faster pace thus providing a boost in speed/performance.
Later Generations
Beyond the third generation, there have been a number of later generations, based on advances in ‘integrated circuit’ technology.
With the rapid pace of technology, the high rate of introduction of new products, and the improvements in software as well as hardware, the classification by generation becomes less clear and less meaningful. (4th generation is Microprocessor and 5th is Artificial Intel)
In the later generations, two most important changes are made in:
- Semiconductor memory
- Microprocessors
